Referring to FIGS. 11A to 13, a conventional electron tube, e.g., a conventional fluorescent display tube, will now be described in detail. Like reference numerals in FIGS. 11A to 13 represent like parts and, if there are a plurality of same elements, only one will be designated by a reference numeral.
FIGS. 11A and 11B show a prior art fluorescent display tube equipped with a plurality of pairs of insulating supports (dampers) such as a metal line coated with an insulator or a glass fiber, wherein the dampers are correspondingly arranged at an upper and a lower side of a cathode filament, respectively, thereby forming a pair (see, for instance, Japanese Patent Laid-Open Publication No. 1984-146139, in particular FIG. 3).
FIGS. 11A and 11B present a cross sectional view seen in a direction indicated by arrows after cutting along a line X2—X2 of FIG. 11B and a top view seen in a direction indicated by arrows after cutting along a line X1—X1 of FIG. 11A, respectively.
The prior art fluorescent display tube includes a front substrate 11 and an anode substrate 12 facing each other. Formed on inner surfaces of the front substrate 11 and the anode substrate 12 are a transparent conductive film 111 and an anode electrode 121 coated with a fluorescent substance, respectively. There are provided between the two substrates 11, 12 a cathode filament 21 and a grid 24 for controlling electrons emitted from the filament 21. The electrons emitted from the cathode filament 21 cause the fluorescent substance of the anode electrode 121 to radiate light.
In case the fluorescent display tube has a lengthy filament 21 or is mounted on an automobile, the filament 21 may vibrate and may come into contact with other components or the substrates of the display tube. In order to prevent such contact, there are disposed a plurality of pairs of dampers 221 and 222, wherein the dampers 221, 222 are correspondingly arranged at the upper and the lower side of the filament 21, respectively. The pairs of dampers are spaced apart from each other at a predetermined interval.
Referring to FIGS. 12A and 12B, there are shown another prior art fluorescent display tube including a front substrate where a plurality of dampers made of a metal line are arranged at one side of a cathode filament (see, for example, Japanese Patent Laid-Open Publication No. 2002-245925, in particular FIG. 5), wherein FIG. 12A is a cross sectional view seen in a direction indicated by arrows after cutting along a line X4—X4 of FIG. 12B; and FIG. 12B is a top view seen from a direction indicated by an arrow X3 shown in FIG. 12A.
The damper 22 made of a metal line is installed at one side of the filament 21, such that one end of the damper 22 is interposed between a metal layer 31 such as an aluminum thin film formed on the front substrate 11 and a metal piece 32 such as an aluminum wire, by an ultrasonic bonding to thereby wedge one end of the damper 22 by the metal layer 31 together with the metal piece 32. The damper 22 has a predetermined vertical position maintained by a use of a spacer 33 made of, e.g., a metal line.
In the first prior art display tube, an issue of how to fix ends of the dampers 221, 222 installed at both sides of the filament 21 is addressed. As one method of fixing the dampers 221, a scheme depicted in FIG. 13 can be conceived by adopting the fixing method of the second prior art display tube shown in FIGS. 12A and 12B (the scheme has not been disclosed).
As illustrated in FIG. 13, a lower damper 221 is fastened to a front substrate 11, while an upper damper 222 is fastened to an anode substrate 12. The damper 221 has both ends fixedly attached to a pair of metal layers 311 together with a corresponding pair of the metal pieces 321 by using the ultrasonic bonding technique. Similar to the damper 221, both ends of the damper 222 are fixedly attached to a pair of metal layers 312 with the metal pieces 322 by the same bonding technique.
In this case, the fixing process of the dampers 221, 222 is repeatedly performed at four locations in the front substrate 11 and the anode substrate 12. For this reason, a space for installing the metal layers 311, 312 and the spacers 331, 332 is enlarged, thereby increasing so-called dead space which is not useful in a display function of the fluorescent display tube. In addition, since manufacture and installation processes of the metal layers 311, 312 and the spacers 331, 332 increase and a large number of members are needed therefor, the production costs of the fluorescent display tube may rise. Further, in case of providing the dampers 221, 222 with wirings, the wirings need to be prepared in the front substrate 11 and the anode substrate 12 separately, which in turn doubles the number of wirings and terminals needed therefor.